Integration and packaging issues are of the main obstacles for the commercialization of micro devices such as radio frequency (RF) microelectromechanical systems (MEMS) micro switches, light-emitting diode (LED) display systems, and MEMS or quartz-based oscillators.
Traditional technologies for transferring of devices include transfer by wafer bonding from a transfer wafer to a receiving wafer. One such implementation is “direct printing” involving one bonding step of an array of devices from a transfer wafer to a receiving wafer, followed by removal of the transfer wafer. Another such implementation is “transfer printing” involving two bonding/de-bonding steps. In transfer printing a transfer wafer may pick up an array of devices from a donor wafer, and then bond the array of devices to a receiving wafer, followed by removal of the transfer wafer.
Some printing process variations have been developed where a device can be selectively bonded and de-bonded during the transfer process. In both traditional and variations of the direct printing and transfer printing technologies, the transfer wafer is de-bonded from a device after bonding the device to the receiving wafer. In addition, the entire transfer wafer with the array of devices is involved in the transfer process.
Conventionally, a method for fabricating a semiconductor die array includes the steps of: (1) growing at a growth temperature within a growth reactor a first semiconductor layer on a foreign growth substrate or a donor substrate; (2) growing at the growth temperature within the growth reactor a second semiconductor layer on the first semiconductor layer; (3) separating by laser lift-off the first semiconductor layer from the growth substrate or the donor substrate so as to form a free-standing semiconductor die; and (4) transferring the free-standing semiconductor die from the donor substrate to a target substrate so as to form an array of the semiconductor die by the direct printing or the transfer printing operation.
The separation of the semiconductor die and the growth substrate can be accomplished in various manners including mechanical grinding, laser lift-off, etching, etc. However, this conventional approach has several limitations. For example, III-nitride deposition process necessitates high temperatures (typically 1000 degrees Celsius to 1100 degrees Celsius). During cooling down from the growth temperature to room temperature, the III-nitride film undergoes a biaxial stress caused by the large difference between the thermal-expansion coefficients of the nitride crystal and the substrate material. This stress can cause cracking, bowing, generation of crystal defects, and other adverse effects.